Mixing unfamiliar pigs causes intense fighting that may last 24-48 hours; regrouping is a major welfare challenge in commercial pig production that management strategies can significantly mitigate.
Pig social hierarchies are established through fighting when strangers meet. Commercial systems that mix pigs from different litters at weaning, fattening, or movement between units impose repeated bouts of social disruption. Beyond the welfare cost of fighting itself, subordinate pigs may be unable to access food and water adequately during the hierarchy establishment period. Stable group management and mixing mitigation strategies represent important welfare improvements.